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Updating user manual

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Daniel Chappuis 2020-05-21 00:20:05 +02:00
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@ -962,6 +962,49 @@ transform.getOpenGLMatrix(matrix);
A nice article to read about this time interpolation is the one from Glenn Fiedler at \url{https://gafferongames.com/post/fix_your_timestep/}. A nice article to read about this time interpolation is the one from Glenn Fiedler at \url{https://gafferongames.com/post/fix_your_timestep/}.
\subsection{Mass, Center of Mass, Inertia Tensor}
\label{sec:rigidbodymass}
The mass, center of mass and inertia tensor of a rigid body are important parameters for the physics simulation.
\subsubsection{Mass}
The \texttt{RigidBody} has a mass value (in kilograms) which is 1 kilogram by default. There are two ways to set the mass of a rigid body. First, you
can set it directly using the \texttt{RigidBody::setMass()} method. Secondly, it is also possible to compute this mass
automatically using the mass of the colliders of the rigid body. As described in section \ref{sec:material}, the material of each collider has a
mass density value. This value is 1 by default. You change change the mass density value of the colliders of a rigid body and then use the
\texttt{RigidBody::updateMassFromColliders()} method to automatically compute the mass of the rigid body using the mass density and shape of
its colliders.
\subsubsection{Center of mass}
The center of mass of a \texttt{RigidBody} is the mean location of the distribution of mass of the body in space. By default the center of mass
of the rigid body is its origin. There are two ways to set the center of mass of a rigid body. First, you can set it directly using the
\texttt{RigidBody::setLocalCenterOfMass()} method. Secondly, as for the mass, the center of mass can also be computed automatically using the
mass, shape and transform of all the colliders of the rigid body. As described in section \ref{sec:material}, the material of each collider has a
mass density value. This value is 1 by default. You can set the mass density value of the colliders and then use the
\texttt{RigidBody::updateLocalCenterOfMassFromColliders()} method to automatically compute the center of mass of the rigid body.
\subsubsection{Inertia Tensor}
\begin{sloppypar}
The inertia tensor of a \texttt{RigidBody} is a $3 \times 3$ matrix describing how the mass is distributed inside the rigid body which is
used to calculate its rotation. The inertia tensor depends on the mass and the shape of the body. There are two ways to set the inertia tensor of
a rigid body. First, you can set it directly using the \texttt{RigidBody::setLocalInertiaTensor()} method. Note that this will set the inertia tensor
of the body in local-space coordinates which is usually a diagonal matrix. This method takes a \texttt{Vector3} with the three diagonal entries of the
matrix. Secondly, the local inertia tensor can be computed automatically using the mass density, shape and transform of all the colliders of the body.
As described in section \ref{sec:material}, the material of each collider has a mass density value which is 1 by default. You can set the mass density
value of the colliders and then use the \texttt{RigidBody::updateLocalInertiaTensorFromColliders()} method to automatically compute the local inertia
tensor of the body.
\end{sloppypar}
\vspace{0.6cm}
\begin{sloppypar}
Note that it is also possible to automatically compute the mass, center of mass and inertia tensor of a rigid body at the same time using the
\texttt{RigidBody::updateMassPropertiesFromColliders()}.
\end{sloppypar}
\subsection{Destroying a Rigid Body} \subsection{Destroying a Rigid Body}
\begin{sloppypar} \begin{sloppypar}
@ -1007,14 +1050,14 @@ collider = body->addCollider(&shape, transform);
\vspace{0.6cm} \vspace{0.6cm}
Note that a given collision shape instance can be shared between multiple colliders. The next section the different types of collision shapes that Note that a given collision shape instance can be shared between multiple colliders. The next section presents the different types of collision
are available in ReactPhysics3D. shapes that are available in ReactPhysics3D.
\subsection{Collision Shapes} \subsection{Collision Shapes}
\label{sec:collisionshapes} \label{sec:collisionshapes}
As we have just seen, the collision shape is used to describe the shape of a collider. They are many types of collision shapes that you can use. They As we have just seen, a collision shape is used to describe the shape of a collider for collision detection. They are many types of
all inherit from the \texttt{CollisionShape} class. collision shapes that you can use. They all inherit from the \texttt{CollisionShape} class.
\subsubsection{Box Shape} \subsubsection{Box Shape}
@ -1024,18 +1067,19 @@ collider = body->addCollider(&shape, transform);
\label{fig:boxshape} \label{fig:boxshape}
\end{figure} \end{figure}
The \texttt{BoxShape} class describes a box collision shape. The box is aligned with the shape local X, Y and Z axis. The \texttt{BoxShape} class describes a box collision shape centered at the origin of the collider. The box is aligned with the shape
In order to create a box shape, you only need to specify the three half extents dimensions of the box in the three X, Y and Z directions. \\ local X, Y and Z axis. In order to create a box shape, you only need to specify the three half extents dimensions of the box in the three X, Y and
Z directions. \\
For instance, if you want to create a box shape with dimensions of 4 meters, 6 meters and 10 meters along the X, Y and Z axis respectively, you need to use the For instance, if you want to create a box shape with dimensions of 4 meters, 6 meters and 10 meters along the X, Y and Z axis respectively, you
following code: \\ need to use the following code: \\
\begin{lstlisting} \begin{lstlisting}
// Half extents of the box in the x, y and z directions // Half extents of the box in the x, y and z directions
const rp3d::Vector3 halfExtents(2.0, 3.0, 5.0); const Vector3 halfExtents(2.0, 3.0, 5.0);
// Create the box shape // Create the box shape
const rp3d::BoxShape boxShape(halfExtents); BoxShape* boxShape = phycsicsCommon.createBoxShape(halfExtents);
\end{lstlisting} \end{lstlisting}
\vspace{0.6cm} \vspace{0.6cm}
@ -1048,13 +1092,14 @@ const rp3d::BoxShape boxShape(halfExtents);
\label{fig:sphereshape} \label{fig:sphereshape}
\end{figure} \end{figure}
The \texttt{SphereShape} class describes a sphere collision shape centered at the origin of the shape local space. You only need to specify the radius of the sphere to create it. \\ The \texttt{SphereShape} class describes a sphere collision shape centered at the origin of the collider. You only need to specify the
radius of the sphere to create it. \\
For instance, if you want to create a sphere shape with a radius of 2 meters, you need to use the following code: \\ For instance, if you want to create a sphere shape with a radius of 2 meters, you need to use the following code: \\
\begin{lstlisting} \begin{lstlisting}
// Create the sphere shape with a radius of 2m // Create the sphere shape with a radius of 2m
const rp3d::SphereShape sphereShape(2.0); SphereShape* sphereShape = physicsCommon.createSphereShape(2.0);
\end{lstlisting} \end{lstlisting}
\vspace{0.6cm} \vspace{0.6cm}
@ -1067,15 +1112,15 @@ const rp3d::SphereShape sphereShape(2.0);
\label{fig:capsuleshape} \label{fig:capsuleshape}
\end{figure} \end{figure}
The \texttt{CapsuleShape} class describes a capsule collision shape around the local Y axis and centered at the origin of the shape local-space. It is the convex hull of two The \texttt{CapsuleShape} class describes a capsule collision shape around the local Y axis and centered at the origin of the collider.
spheres. It can also be seen as an elongated sphere. In order to create it, you only need to specify the radius of the two spheres and the height of the It is the convex hull of two spheres. It can also be seen as an elongated sphere. In order to create it, you only need to specify the
capsule (distance between the centers of the two spheres). \\ radius of the two spheres and the height of the capsule (distance between the centers of the two spheres). \\
For instance, if you want to create a capsule shape with a radius of 1 meter and the height of 2 meters, you need to use the following code: \\ For instance, if you want to create a capsule shape with a radius of 1 meter and the height of 2 meters, you need to use the following code: \\
\begin{lstlisting} \begin{lstlisting}
// Create the capsule shape // Create the capsule shape
const rp3d::CapsuleShape capsuleShape(1.0, 2.0); CapsuleShape* capsuleShape = physicsCommon.createCapsuleShape(1.0, 2.0);
\end{lstlisting} \end{lstlisting}
\vspace{0.6cm} \vspace{0.6cm}
@ -1088,13 +1133,15 @@ const rp3d::CapsuleShape capsuleShape(1.0, 2.0);
\label{fig:convexshape} \label{fig:convexshape}
\end{figure} \end{figure}
The \texttt{ConvexMeshShape} class can be used to describe the shape of a convex mesh. In order to create a convex mesh shape, you first need to create an array of \texttt{PolygonFace} to describe each face The \texttt{ConvexMeshShape} class can be used to describe the shape of a convex mesh centered at the origin of the collider. In order to create a
of your mesh. You also need to have an array with the vertices coordinates and an array with the vertex indices of each face of you mesh. Then, you have to create a \texttt{PolygonVertexArray} with your convex mesh shape, you first need to create an array of \texttt{PolygonFace} to describe each face of your mesh. You also need to have an array with
vertices coordinates and indices array. You also need to specify your array of \texttt{PolygonFace}. Then, you have to create a \texttt{PolyhedronMesh} with your \texttt{PolygonVertexArray}. the vertices coordinates and an array with the vertex indices of each face of you mesh. Then, you have to create a \texttt{PolygonVertexArray} with
Once this is done, you can create the \texttt{ConvexMeshShape} by passing your \texttt{PolyhedronMesh} in paramater. \\ your vertices coordinates and indices array. You also need to specify your array of \texttt{PolygonFace}. Then, you have to create a
\texttt{PolyhedronMesh} with your \texttt{PolygonVertexArray}. Once this is done, you can create the \texttt{ConvexMeshShape} by passing your
\texttt{PolyhedronMesh} in paramater. \\
The following example shows how to create a convex mesh shape. In this example, we create a cube as a convex mesh shape. Of course, this is only for the example. The following example shows how to create a convex mesh shape. In this example, we create a cube as a convex mesh shape. Of course, this is only
If you really need a cube collision shape, you should use the \texttt{BoxShape} instead. \\ for the example. If you really need a cube collision shape, you should use the \texttt{BoxShape} instead. \\
\begin{lstlisting} \begin{lstlisting}
// Array with the vertices coordinates of the convex mesh // Array with the vertices coordinates of the convex mesh
@ -1118,8 +1165,8 @@ indices[16]=2; indices[17]=3; indices[18]=7; indices[19]=6;
indices[20]=0; indices[21]=4; indices[22]=7; indices[23]=3; indices[20]=0; indices[21]=4; indices[22]=7; indices[23]=3;
// Description of the six faces of the convex mesh // Description of the six faces of the convex mesh
polygonFaces = new rp3d::PolygonVertexArray::PolygonFace[6]; polygonFaces = new PolygonVertexArray::PolygonFace[6];
rp3d::PolygonVertexArray::PolygonFace* face = polygonFaces; PolygonVertexArray::PolygonFace* face = polygonFaces;
for (int f = 0; f < 6; f++) { for (int f = 0; f < 6; f++) {
// First vertex of the face in the indices array // First vertex of the face in the indices array
@ -1132,35 +1179,36 @@ for (int f = 0; f < 6; f++) {
} }
// Create the polygon vertex array // Create the polygon vertex array
polygonVertexArray = new rp3d::PolygonVertexArray(8, vertices, 3 x sizeof(float), PolygonaVertexArray* polygonVertexArray = new PolygonVertexArray(8, vertices, 3 x sizeof(float),
indices, sizeof(int), 6, polygonFaces, indices, sizeof(int), 6, polygonFaces,
rp3d::PolygonVertexArray::VertexDataType::VERTEX_FLOAT_TYPE, PolygonVertexArray::VertexDataType::VERTEX_FLOAT_TYPE,
rp3d::PolygonVertexArray::IndexDataType::INDEX_INTEGER_TYPE); PolygonVertexArray::IndexDataType::INDEX_INTEGER_TYPE);
// Create the polyhedron mesh // Create the polyhedron mesh
polyhedronMesh = new rp3d::PolyhedronMesh(polygonVertexArray); PolyhedronMesh* polyhedronMesh = physicsCommon.createPolyhedronMesh(polygonVertexArray);
// Create the convex mesh collision shape // Create the convex mesh collision shape
convexMeshShape = new rp3d::ConvexMeshShape(polyhedronMesh); ConvexMeshShape* convexMeshShape = physicsCommon.createConvexMeshShape(polyhedronMesh);
\end{lstlisting} \end{lstlisting}
\vspace{0.6cm} \vspace{0.6cm}
Note that the vertex coordinates and indices array are not copied and therefore, you need to make sure that they exist until the collision shape exists. This is also true for Note that the vertex coordinates and indices array are not copied and therefore, you need to make sure that they exist until the collision shape
the all the \texttt{PolygonFace}, the \texttt{PolygonVertexArray} and the \texttt{PolyhedronMesh}. \\ exists. This is also true for the all the \texttt{PolygonFace}, the \texttt{PolygonVertexArray} and the \texttt{PolyhedronMesh}. \\
You need to make sure that the mesh you provide is indeed convex. Secondly, you should provide the simplest possible convex mesh. It means that you need to avoid You need to make sure that the mesh you provide is indeed convex. Secondly, you should provide the simplest possible convex mesh. It means
coplanar faces in your convex mesh shape. Coplanar faces have to be merged together. Remember that convex meshes are not limited to triangular faces, you can that you need to avoid coplanar faces in your convex mesh shape. Coplanar faces have to be merged together. Remember that convex meshes are
create faces with more than three vertices. \\ not limited to triangular faces, you can create faces with more than three vertices. \\
When you specify the vertices for each face of your convex mesh, be careful with their order. The vertices of a face must be specified in counter clockwise order When you specify the vertices for each face of your convex mesh, be careful with their order. The vertices of a face must be specified in
as seen from the outside of your convex mesh. \\ counter clockwise order as seen from the outside of your convex mesh. \\
You also need to make sure that the origin of your mesh is inside the convex mesh. A mesh with an origin outside the You also need to make sure that the origin of your mesh is inside the convex mesh. A mesh with an origin outside the
convex mesh is not currently supported by the library. \\ convex mesh is not currently supported by the library. \\
You can also specify a scaling factor in the constructor when you create a \texttt{Convex\allowbreak MeshShape}. All the vertices of your mesh will be scaled from the origin by this factor You can also specify a scaling factor in the constructor when you create a \texttt{Convex\allowbreak MeshShape}. All the vertices of your mesh
when used in the collision shape. \\ will be scaled from the origin by this factor when used in the collision shape. It means that you can use the same \texttt{PolyhedronMesh} for
multiple \texttt{ConvexMeshShape} with a different scaling factor each time. \\
Note that collision detection with a \texttt{ConvexMeshShape} is more expensive than with a \texttt{SphereShape} or a \texttt{CapsuleShape}. \\ Note that collision detection with a \texttt{ConvexMeshShape} is more expensive than with a \texttt{SphereShape} or a \texttt{CapsuleShape}. \\
@ -1192,11 +1240,11 @@ const int nbVertices = 8;
const int nbTriangles = 12; const int nbTriangles = 12;
float vertices[3 * nbVertices] = ...; float vertices[3 * nbVertices] = ...;
int indices[3 * nbTriangles] = ...; int indices[3 * nbTriangles] = ...;
rp3d::TriangleVertexArray* triangleArray = TriangleVertexArray* triangleArray =
new rp3d::TriangleVertexArray(nbVertices, vertices, 3 * sizeof(float), nbTriangles, new TriangleVertexArray(nbVertices, vertices, 3 * sizeof(float), nbTriangles,
indices, 3 * sizeof(int), indices, 3 * sizeof(int),
rp3d::TriangleVertexArray::VertexDataType::VERTEX_FLOAT_TYPE, TriangleVertexArray::VertexDataType::VERTEX_FLOAT_TYPE,
rp3d::TriangleVertexArray::IndexDataType::INDEX_INTEGER_TYPE); TriangleVertexArray::IndexDataType::INDEX_INTEGER_TYPE);
\end{lstlisting} \end{lstlisting}
\vspace{0.6cm} \vspace{0.6cm}
@ -1205,13 +1253,13 @@ rp3d::TriangleVertexArray::IndexDataType::INDEX_INTEGER_TYPE);
into it as a subpart. Once this is done, we can create the actual \texttt{ConcaveMeshShape}. \\ into it as a subpart. Once this is done, we can create the actual \texttt{ConcaveMeshShape}. \\
\begin{lstlisting} \begin{lstlisting}
rp3d::TriangleMesh triangleMesh; TriangleMesh triangleMesh* = physicsCommon.createTriangleMesh();
// Add the triangle vertex array to the triangle mesh // Add the triangle vertex array to the triangle mesh
triangleMesh.addSubpart(triangleArray); triangleMesh->addSubpart(triangleArray);
// Create the concave mesh shape // Create the concave mesh shape
ConcaveMeshShape* concaveMesh = new rp3d::ConcaveMeshShape(&triangleMesh); ConcaveMeshShape* concaveMesh = physicsCommon.createConcaveMeshShape(triangleMesh);
\end{lstlisting} \end{lstlisting}
\vspace{0.6cm} \vspace{0.6cm}
@ -1222,8 +1270,11 @@ ConcaveMeshShape* concaveMesh = new rp3d::ConcaveMeshShape(&triangleMesh);
When you specify the vertices for each triangle face of your mesh, be careful with the order of the vertices. They must be specified in counter clockwise order When you specify the vertices for each triangle face of your mesh, be careful with the order of the vertices. They must be specified in counter clockwise order
as seen from the outside of your mesh. \\ as seen from the outside of your mesh. \\
You can also specify a scaling factor in the constructor when you create a \texttt{Concave\allowbreak MeshShape}. All the vertices of your mesh will be scaled from the origin by this factor \begin{sloppypar}
when used in the collision shape. \\ You can also specify a scaling factor in the \texttt{PhysicsCommon::createConcaveMeshShape()} when you create a \texttt{Concave\allowbreak MeshShape}.
All the vertices of your mesh will be scaled from the origin by this factor when used in the collision shape. It means that you can use the same
\texttt{TriangleMesh} for multiple \texttt{ConcaveMeshShape} with a different scaling factor each time. \\
\end{sloppypar}
In the previous example, the vertex normals that are needed for collision detection are automatically computed. However, if you want to specify your own In the previous example, the vertex normals that are needed for collision detection are automatically computed. However, if you want to specify your own
vertex normals, you can do it by using another constructor for the \texttt{TriangleVertexArray}. \\ vertex normals, you can do it by using another constructor for the \texttt{TriangleVertexArray}. \\
@ -1264,7 +1315,7 @@ float maxHeight = 500;
float heightValues[nbRows * nbColumns] = ...; float heightValues[nbRows * nbColumns] = ...;
// Create the heightfield collision shape // Create the heightfield collision shape
rp3d::HeightFieldShape = new rp3d::HeightFieldShape(nbColumns, nbRows, minHeight, HeightFieldShape* heightFieldShape = physicsCommon.createHeightFieldShape(nbColumns, nbRows, minHeight,
maxHeight, heightValues, rp3d::HeightFieldShape::HEIGHT_FLOAT_TYPE); maxHeight, heightValues, rp3d::HeightFieldShape::HEIGHT_FLOAT_TYPE);
\end{lstlisting} \end{lstlisting}
@ -1274,30 +1325,23 @@ maxHeight, heightValues, rp3d::HeightFieldShape::HEIGHT_FLOAT_TYPE);
they exist during the lifetime of the \texttt{HeightField\allowbreak Shape} and you must not forget to release their memory when you they exist during the lifetime of the \texttt{HeightField\allowbreak Shape} and you must not forget to release their memory when you
destroy the collision shape or at the end of your application. \\ destroy the collision shape or at the end of your application. \\
You can also specify a scaling factor in the constructor when you create a \texttt{Height\allowbreak FieldShape}. All the vertices of your mesh will be scaled from the origin by this factor You can also specify a scaling factor in the \texttt{PhysicsCommon::createHeightShape()} method when you create a \texttt{Height\allowbreak FieldShape}.
when used in the collision shape. \\ All the vertices of your mesh will be scaled from the origin by this factor when used in the collision shape. \\
When creating a \texttt{HeightFieldShape}, the origin of the shape will be at the center of its bounding volume. When creating a \texttt{HeightFieldShape}, the origin of the shape will be at the center of its bounding volume.
Therefore, if you create a \texttt{HeightFieldShape} with a minimum height of 100 and a maximum height of 500, the Therefore, if you create a \texttt{HeightFieldShape} with a minimum height of 100 and a maximum height of 500, the
maximum coordinates of the shape on the Y axis will be 200 and the minimum coordinates will be -200. maximum coordinates of the shape on the Y axis will be 200 and the minimum coordinates will be -200.
\subsection{Mass, Center of Mass, Inertia Tensor}
\label{sec:collidermass}
Note that the inertia tensor
is a $3 \times 3$ matrix describing how the mass is distributed inside the rigid body which will be used to calculate its rotation. The inertia
tensor depends on the mass and the shape of the body.
\subsection{Collision filtering} \subsection{Collision filtering}
\label{sec:collisionfiltering} \label{sec:collisionfiltering}
By default all the collision shapes of all your bodies are able to collide with each other in the world. However, sometimes we want a body to collide only with a given By default all the colliders of the bodies are able to collide with each other in the world. However, sometimes we want a body to collide only
group of bodies and not with other bodies. This is called collision filtering. The idea is to group the collision shapes of bodies into categories. Then we can specify with a given group of bodies and not with other bodies. This is called collision filtering. The idea is to group the colliders of bodies into
for each collision shape against which categories it will be able to collide. \\ categories. Then we can specify for each collider against which categories of colliders it will be able to collide. \\
ReactPhysics3D uses bits mask to represent categories. The first thing to do is to assign a category to the collision shapes of your body. To do this, you need to ReactPhysics3D uses bits masks to represent categories. The first thing to do is to assign a category to the colliders of your body. To do
call the \texttt{ProxyShape::setCollisionCategoryBits()} method on the corresponding proxy shape as in the following example. Here we consider that we have four bodies this, you need to call the \texttt{Collider::setCollisionCategoryBits()} method on the corresponding collider as in the following example. Here
where each one has a single collision shape. \\ we consider that we have four bodies where each one has a single collider. \\
\begin{lstlisting} \begin{lstlisting}
// Enumeration for categories // Enumeration for categories
@ -1308,59 +1352,71 @@ enum Category {
}; };
// Set the collision category for each proxy shape of // Set the collision category for each collider of
// each of the four bodies // each of the four bodies
proxyShapeBody1->setCollisionCategoryBits(CATEGORY1); colliderBody1->setCollisionCategoryBits(CATEGORY1);
proxyShapeBody2->setCollisionCategoryBits(CATEGORY2); colliderBody2->setCollisionCategoryBits(CATEGORY2);
proxyShapeBody3->setCollisionCategoryBits(CATEGORY3); colliderBody3->setCollisionCategoryBits(CATEGORY3);
proxyShapeBody4->setCollisionCategoryBits(CATEGORY3); colliderBody4->setCollisionCategoryBits(CATEGORY3);
\end{lstlisting} \end{lstlisting}
\vspace{0.6cm} \vspace{0.6cm}
As you can see, the collision shape of body 1 will be part of the category 1, the collision shape of body 2 will be part of the category 2 and the collision shapes of bodies 3 and 4 will be As you can see, the collider of body 1 will be part of the category 1, the collider of body 2 will be part of the category 2 and the colliders of
part of the category 3. \\ bodies 3 and 4 will be part of the category 3. \\
\begin{sloppypar} \begin{sloppypar}
Now, for each collision shape, we need to specify with which categories the shape is allowed to collide with. To do this, you need to use the \texttt{ProxyShape::setCollideWithMaskBits()} Now, for each collider, we need to specify with which categories it is allowed to collide with. To do this, you need to use the
method of the proxy shape. Note that you can specify one or more categories using the bitwise OR operator. The following example shows how to specify with which categories the \texttt{Collider::setCollideWithMaskBits()} method. Note that you can specify one or more categories using the bitwise OR operator. The
shapes can collide. \\ following example shows how to specify with which categories the collider can collide. \\
\end{sloppypar} \end{sloppypar}
\begin{lstlisting} \begin{lstlisting}
// For each shape, we specify with which categories it // For each collider, we specify with which categories it
// is allowed to collide // is allowed to collide
proxyShapeBody1->setCollideWithMaskBits(CATEGORY3); colliderBody1->setCollideWithMaskBits(CATEGORY3);
proxyShapeBody2->setCollideWithMaskBits(CATEGORY1 | CATEGORY3); colliderBody2->setCollideWithMaskBits(CATEGORY1 | CATEGORY3);
proxyShapeBody3->setCollideWithMaskBits(CATEGORY2); colliderBody3->setCollideWithMaskBits(CATEGORY2);
proxyShapeBody4->setCollideWithMaskBits(CATEGORY2); colliderBody4->setCollideWithMaskBits(CATEGORY2);
\end{lstlisting} \end{lstlisting}
\vspace{0.6cm} \vspace{0.6cm}
As you can see, we specify that the body 1 will be allowed to collide with bodies from the categorie 3. We also indicate that the body 2 will be allowed to collide with bodies from the As you can see, we specify that the body 1 will be allowed to collide with bodies from the categorie 3. We also indicate that the body 2 will be
category 1 and 3 (using the bitwise OR operator). Finally, we specify that bodies 3 and 4 will be allowed to collide against bodies of the category 2. \\ allowed to collide with bodies from the category 1 and 3 (using the bitwise OR operator). Finally, we specify that bodies 3 and 4 will be allowed
to collide against bodies of the category 2. \\
A collision shape is able to collide with another only if you have specify that the category mask of the first shape is part of the \emph{collide with} mask of the second shape. It A collider is able to collide with another only if you have specify that the category mask of the first collider is part of the
is also important to understand that this condition must be satisfied in both directions. For instance in the previous example, the body 1 (of category 1) says that it wants to collide \emph{collide with} mask of the second collider. It is also important to understand that this condition must be satisfied in both directions. For
against bodies of the category 3 (for instance against body 3). However, body 1 and body 3 will not be able to collide because the body 3 does not say that it wants to collide instance in the previous example, the body 1 (of category 1) says that it wants to collide against bodies of the category 3 (for instance against
with bodies from category 1. Therefore, in the previous example, the body 2 is allowed to collide against bodies 3 and 4 but no other collision is allowed. \\ body 3). However, body 1 and body 3 will not be able to collide because the body 3 does not say that it wants to collide
with bodies from category 1. Therefore, in the previous example, the body 2 is allowed to collide against bodies 3 and 4 but no other collision
is allowed. \\
In the same way, you can perform this filtering for ray casting (described in section \ref{sec:raycasting}). For instance, you can perform a ray cast test In the same way, you can perform this filtering for ray casting (described in section \ref{sec:raycasting}). For instance, you can perform a ray cast test
against a given subset of categories of collision shapes only. against a given subset of categories of collision shapes only.
\subsection{Material of a Rigid Body} \subsection{Material}
\label{sec:material}
The material of a rigid body is used to describe the physical properties it is made of. This is represented by the \texttt{Material} class. Each body that The material of a rigid body is used to describe the physical properties it is made of. This is represented by the \texttt{Material} class. Each body that
you create will have a default material. You can get the material of the rigid body using the \texttt{RigidBody::\allowbreak getMaterial()} method. Then, you will be able to change some you create will have a default material. You can get the material of the rigid body using the \texttt{RigidBody::\allowbreak getMaterial()} method. \\
properties. \\
For instance, you can change the bounciness of the rigid body. The bounciness is a value between 0 and 1. The value 1 is used for a very bouncy object and the value 0 means that You can use the material to set those physical properties. \\
the body will not be bouncy at all. To change the bounciness of the material, you can use the \texttt{Material::\allowbreak setBounciness()} method. \\
You are also able to change the friction coefficient of the body. This value needs to be between 0 and 1. If the value is 0, no friction will be applied when the body is in contact with For instance, you can change the bounciness of the rigid body. The bounciness is a value between 0 and 1. The value 1 is used for a very bouncy
another body. However, if the value is 1, the friction force will be high. You can change the friction coefficient of the material with the object and the value 0 means that the body will not be bouncy at all. To change the bounciness of the material, you can use the
\texttt{Material::\allowbreak setFrictionCoefficient()} method. \\ \texttt{Material::\allowbreak setBounciness()} method. \\
\begin{sloppypar}
It is also possible to set the mass density of the collider which has a default value of 1. As described in section \label{sec:rigidbodymass}, the
mass density of a collider can be used to automatically compute the mass, center of mass and inertia tensor of a rigid body. In order to change the
mass density of a collider, you need to use the \texttt{Material::setMassDensity()} method. \\
\end{sloppypar}
You are also able to change the friction coefficient of the body. This value needs to be between 0 and 1. If the value is 0, no friction will be
applied when the body is in contact with another body. However, if the value is 1, the friction force will be high. You can change the
friction coefficient of the material with the \texttt{Material::\allowbreak setFrictionCoefficient()} method. \\
You can use the material to add rolling resistance to a rigid body. Rolling resistance can be used to stop You can use the material to add rolling resistance to a rigid body. Rolling resistance can be used to stop
a rolling object on a flat surface for instance. You should use this only with SphereShape or a rolling object on a flat surface for instance. You should use this only with SphereShape or
@ -1371,13 +1427,13 @@ proxyShapeBody4->setCollideWithMaskBits(CATEGORY2);
\begin{lstlisting} \begin{lstlisting}
// Get the current material of the body // Get the current material of the body
rp3d::Material& material = rigidBody->getMaterial(); Material& material = rigidBody->getMaterial();
// Change the bounciness of the body // Change the bounciness of the body
material.setBounciness(rp3d::decimal(0.4)); material.setBounciness(0.4);
// Change the friction coefficient of the body // Change the friction coefficient of the body
material.setFrictionCoefficient(rp3d::decimal(0.2)); material.setFrictionCoefficient(0.2);
\end{lstlisting} \end{lstlisting}
\section{Joints} \section{Joints}